Intro to Quantities Review Problems

These are the calculations you should be able to perform:• Sum of molar mass for a compound• Convert mass mole• Convert mole mass• Convert mole number of particles• Convert number of particles mole• Convert mole gas volume at STP• Convert gas volume at STP mole• Determine gas density from molar mass at STP• Determine molar mass from gas density at STP• Determine % composition of a compound• Determine empirical & molecular formula given composition data

These steps can be combined into 2 step conversions

Intro to Quantities Review Problems

One-step conversions

Convert 25.5 grams of potassium chloride to moles.

Convert 0.334 moles of hydrochloric acid to mass in grams.

25.5 g KCl 74.551 g

KCl

1 mol KCl= 0.342 mol KCl

0.334 mol HCl

36.461g HCl1 mol HCl

= 12.2 g HCl

Put molar mass here

Put 1 mole here

Divide÷

Put molar mass here

Put 1 mole here

MultiplyX

Intro to Quantities Review Problems

One-step conversions

Convert 3.50x1024 molecules of H2O to moles.

Convert 5.77 moles of nitric acid to the number of molecules.

3.50x1024 molec. H2O

6.02x1023 molecules

1 mol H2O= 5.81 mol H2O

5.77 mol HNO3

6.02x1023 molecules HNO3 1 mol

HNO3

= 3.47x1024 molec. HNO3

Intro to Quantities Review Problems

One-step conversions

Convert 12.2 liters of carbon dioxide gas at STP to moles.

Convert 0.0185 moles of nitrogen gas to volume in liters at STP.

12.2 L CO2 22.4 L CO2

1 mol CO2= 0.545 mol CO2

0.0185 mol N2

22.4 L N2

1 mol N2

= 0.414 L N2

Intro to Quantities Review Problems

Two-step conversions

Convert 4.22 liters of oxygen gas at STP to mass in grams.

Convert 0.802 grams of chlorine gas to volume in liters at STP.

4.22 L O2

22.4 L O2

1 mol O2 1 mol

O2

31.9988 g O2 = 6.03 g O2

0.802 g Cl2

70.906 g Cl2

1 mol Cl2 1 mol

Cl2

22.4 L Cl2 = 0.253 L Cl2

Intro to Quantities Review Problems

Two-step conversions

Convert 1.00 liter of sulfur dioxide gas at STP to the number of molecules.

Convert 1.00x1022 molecules of nitrogen dioxide gas to the volume in liters at STP.

1.00 L SO2

22.4 L SO2

1 mol SO2 1 mol

SO2

6.02x1023 molec. SO2

= 2.68x1022

molec. SO2

1.00x1022 molec. NO2

6.02x1023 molec. NO2

1 mol NO2

1 mol NO2

22.4 L NO2

= 0.372 L NO2

Intro to Quantities Review Problems

Two-step conversions

Convert 1.00 gram of gold to it’s number of atoms.

Convert 1.00x1023 atoms of mercury to the mass in grams.

1.00 g Au 196.96655g Au

1 mol Au

1 mol Au

6.02x1023 atoms Au= 3.06x1021 atoms Au

1.00x1023 atoms Hg6.02x1023 atoms Hg

1 mol Hg

1 mol Hg

200.59 g Hg = 33.3 g Hg

Intro to Quantities Review Problems

Gas Density Conversions

Determine the density of hydrogen sulfide gas at STP.

If a gas has a density of 3.75 g/L at STP, what is its molar mass?

22.4 L H2S

1 mol H2S 1 mol H2S

34.081 g H2S = 1.52 g/L H2S

1 L

3.75 g

1 mol

22.4 L= 84.0 g/mol

Intro to Quantities Review Problems

Percent Composition

Determine the percent oxygen in zinc oxide.

Determine the percent nitrogen in ammonium phosphate.

% oxygen = ZnO

OX 100=

81.408 g ZnO

15.9994 g OX 100= 19.7%

O

% N = (NH4)3PO4

N x 3X 100=

149.09 g/mol

42.02 g/mol X 100= 28.2% N

Intro to Quantities Review Problems

Empirical & Molecular Formula

Determine the empirical formula of caffeine if its composition is 49.48% C; 5.19% H; 28.85% N; 16.48% O

Determine the molecular formula if the molar mass is 194.2 g/mol

49.48%C 49.48gC

5.19%H 5.19gH

28.85%N 28.85gN

16.48%O 16.48gO

1 mol C

1 mol H

1 mol N

1 mol O

12.011g C

1.00794 g H

14.0067 g N

15.9994 g O

=4.1196 mol

=5.1491 mol

=2.0597 mol

=1.0300 mol

÷1.0300 mol

÷1.0300 mol

÷1.0300 mol

÷1.0300 mol

= 4.00

= 5.00

= 2.00

= 1.00

Empirical

formula:

C4H5N2O

Molecular Formula = Empirical formula

Mol. Mass

Emp. Mass=C4H5N2

O

194.2 g/mol97.10 g/mol

= C8H10N4O2